There is nothing wrong with VB.Net. But it isn't for everyone. Many users of the classic VB6 programming language didn't migrate (for various reasons - lack of backwards compatibility, loss of trust in Microsoft, limited .Net functionality in it's early years, and others).
The lack of backwards compatibility meant you have to continue to support legacy apps (there was no business case for rewriting them, just to have a different language), so little reason to move to .Net.
And if you did move from VB6 what language would you choose knowing Microsoft had just abandoned you and would be likely to do so again ?
So there would be little reason now for VB6 users to move to VB.Net just to be able to use it to write iOS and Android apps using Xamarin, or to use your WebAssembly suggestion to write Web apps.
WebAssembly itself looks interesting, and if VB6 were made so that you could build applications to run in a browser using WebAssembly this would be very acceptable. I suggest it would be easier to do this for VB6 than .Net.